1997
Shear Markers

The introduction of the 3D VIPIR system in 1997 opened new avenues for counteracting the problems we'd encountered when NIDS tables were used for storm tracking, such as:

• A focus on the centroid location rather than that of the actual threat
• A 5-minute delay in receiving attribute information
• Difficulty in relating the threat to the viewer (velocity product)

The necessary improvements involved proprietary processing of every radial from every NEXRAD site in the country, a major effort for the company. The process compared every pixel of radial and storm relative velocity data to corresponding pixels. When the sum of an inbound pixel and a neighboring outbound pixel exceeded 50 knots, the system placed a circle, called a shear marker, over the site.

Shear markers pinpoint the location of potential tornadic circulations with unprecedented precision.

In order to measure the vertical development of storms, all four NEXRAD tilt levels then available were used, creating the potential for as many as six shear markers per radar site. That's a lot. So to help users identify from which product the shear was derived, we decided to place either one or two tick marks at the bottom of a shear marker to depict radial or storm relative shear, and two to four tick marks at the top of the shear marker to indicate at which tilt level the shear was detected.

Also, we enabled users to set only specific types of shear markers to appear, which prevents the display from becoming confusingly cluttered, and allows meteorologists to focus on the areas of greatest concern.

These things meant that off-air, there was instant identification of relative shear and vertical development dealing with the actual threat area rather than centroid, depicted instantly and for the first time. And on-air, by dropping all but low-level shear locks, users could instantly and accurately provide viewers with an easily understood area of threat.

Unless there was ground truth, we urged users—and still do, actually—to tell viewers that the markers indicated a dangerous twisting of the winds, and not necessarily a tornado. If a tornado was present inside a storm, then the spinning marker identifies the likely location.

We chose circular icons because a spinning circle on the map intuitively visualizes both the type of threat and its precise location, which made the shear markers a powerful automated tool. The vast majority of viewers still have zero understanding of Radial or Storm Relative Velocities, but a spinning circle instantly visualizes both the type of threat, a dangerous twisting of the winds, and its precise location. Also for the first time, broadcast meteorologists could click the automated attribute storm track, describe where the majority of rain and hail would be, then shift the SCIT to the center of the shear marker to describe where the greatest threat for tornadoes was.

A simple click of an NWS attribute combines NIDS data with Baron Services' storm tracking technology.